Charging and discharging control circuit and charging type power supply device

ABSTRACT

There are provided a charging and discharging control circuit and a charging type power supply device, which are capable of switching between a normal state and a test state without adding an external terminal for testing. A detection circuit for detecting a voltage higher than an over-charge detection voltage of a secondary battery is provided in the charging and discharging control circuit. A voltage higher than the over-charge detection voltage is applied to a battery connection terminal of the charging and discharging control circuit to switch between a normal application state and the test state. A fuse is further provided in the charging and discharging control circuit to switch between two delay time shortening modes for testing according to the presence or absence of the fuse.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a charging and discharging controlcircuit and a charging type power supply device, which are used for asecondary battery, and more particularly to a test function forevaluating a characteristic of the charging and discharging controlcircuit.

2. Description of the Related Art

A lithium ion secondary battery that has significantly contributed tothe widespread use of portable devices which are represented by a mobiletelephone and a personal handy-phone system (PHS) is characterized by asmall size, light weight, and a large capacity. Therefore, the long-timedrive of the portable device and a reduction in weight thereof arerealized. However, because the charging and discharging of the secondarybattery are repeated, the secondary battery is more likely to be put inan over-charge state or an over-discharge state becomes higher. When thebattery is put in the over-charge state, a battery temperatureincreases. Then, a gas is generated by the decomposition of anelectrolyte solution, so that an internal pressure of the batteryincreases or metal of Li is precipitated. Thus, there is a fear ofignition or burst. In contract to this, when the battery is put in theover-discharge state, the electrolyte solution is decomposed todeteriorate the characteristic of the battery. In order to prevent theoccurrences of such states, a protection circuit is incorporated in abattery pack.

According to a fundamental technique of the protection circuit, acharging and discharging control switch circuit is provided on acharging and discharging path between the secondary battery and the mainbody of the portable device. When a charging and discharging controlcircuit detects a state in which the secondary battery is charged with avoltage equal to or higher than a predetermined voltage, a state inwhich the secondary battery is discharged with a voltage equal to orlower than a predetermined voltage, or a state in which the secondarybattery is discharged with an excessive current, the charging anddischarging control switch circuit is turned OFF to prevent theover-charge state, the over-discharge state, and an over-current statefrom occurring.

The lithium ion secondary battery has a high internal impedance.Therefore, a battery voltage appears to change according to charging anddischarging currents. While the charging current is flowing, the batteryvoltage appears to be high. While the discharging current is flowing,the battery voltage appears to be low. When the battery is efficientlyused, it is necessary to set an over-charge detection delay time and anover-discharge detection delay time. When false cancellation caused by anoise is prevented, it is necessary to set a cancel delay time. Forexample, JP 2001-283932 A (pages 1 to 6 and FIG. 1) discloses that thedelay times are set by an internal delay circuit to shorten test timesfor over-charging and over-discharging. The internal delay circuitprovides all delay times. Thus, it is unnecessary to provide externalcapacitors for determining delay times, so that the number of externalparts of the protection circuit can be reduced.

However, in a charging and discharging control circuit using theinternal delay circuit, the delay times are hard to change from theoutside. The evaluation of the characteristic of the charging anddischarging control circuit takes enormous amounts of test time becauseof the influence of the delay times. The over-current detection delaytime and the over-discharge detection delay time each are generallyabout several milliseconds to 100 milliseconds, so that the test time isnot significantly influenced by the delay time. Because the over-chargedetection delay time is generally set to about several seconds, the testtakes a long time. Therefore, it is necessary for the charging anddischarging control circuit using the internal delay circuit to set atest mode for shortening the delay times.

JP 2001-283932 A discloses a charging and discharging control circuitand a charging type power supply device, in which a test mode forshortening the delay times in the internal control circuit is set when avoltage equal to or higher than a specified voltage is applied between acharger connection terminal. FIG. 2 shows such a circuit example. Whenthe battery is put in the over-charge state, an output of an over-chargedetection comparator 213 becomes a high level and an internal controlcircuit 220 outputs a control signal to an internal delay circuit 221.The internal delay circuit 221 receives an output voltage (controlsignal) from the internal control circuit 220 as an input signal andoutputs a signal for controlling a switch circuit 202 after the lapse ofa specified delay time t1.

When a voltage of an over-current detection terminal becomes equal to orhigher than a specified voltage V1, an output of a voltage detectioncomparator 215 becomes a high level. When the output of the voltagedetection comparator 215 is the high level, the internal control circuit220 enters a state of outputting a control signal for shortening a delaytime of the internal delay circuit 221, and holds the state. When thebattery is put in the over-charge state, the output of the over-chargedetection comparator 213 becomes a high level and the internal controlcircuit 220 outputs the control signal to the internal delay circuit221. The internal delay circuit 221 receives the output voltage (controlsignal) from the internal control circuit 220 as an input signal andoutputs the signal for controlling the switch circuit 202 after thelapse of a specified delay time t2. For that reason, once a voltageapplied to the over-current detection terminal reaches the voltage V1equal to or higher than the specified voltage, the short delay time ismaintained. After that, an over-charge detection voltage can be measuredin a state where the over-charge delay time is short.

When the voltage of the over-current detection terminal becomes equal toor lower than a specified voltage V2, an output of a voltage detectioncomparator 214 becomes a high level. When the output of the voltagedetection comparator 214 is the high level, the internal control circuit220 cancels the state of outputting the control signal for shorteningthe delay time of the internal delay circuit 221 to set the normal delaytime t1. Therefore, once a voltage applied to the over-current detectionterminal becomes the voltage V2 equal to or lower than the specifiedvoltage, the internal control circuit 220 resets the test mode andreturns to a normal state.

However, according to the invention in JP 2001-283932 A, it is necessaryto detect the voltage of the over-current detection terminal at aplurality of levels. According to the above-mentioned technique, thereis a problem in that a circuit structure is complicated and stableoperation is hard to ensure.

In addition, when voltages for detecting the over-charge andover-discharge and for canceling are set in a mass production process,it is necessary to measure detection voltages with precision. At thistime, a wait time equal to or longer than several seconds is requiredevery time an input voltage is stepped up. If the detection voltages canbe detected by 25 steps, a time required for measuring the detectionvoltages becomes 125 seconds in the case where the wait time is assumedto be 5 seconds. Even if the charging and discharging control circuithas a test mode for shortening the delay time to {fraction (1/50)}, themeasurement takes 2.5 seconds per chip. Such measurement takes too longtime in terms of mass production and becomes a serious problem in viewof a test cost.

That is, in the case of initial measurement on a secondary batterycharging and discharging control circuit including a delay circuit,which is performed at the factory, it is necessary to further shortenthe detection delay time. In addition, in the cases of secondarymeasurement and customer's evaluation, both the normal use mode and thetest mode for shortening the delay time are required. It is desired torealize such a control function using few external terminals.

SUMMARY OF THE INVENTION

An object of the present invention is to ensure a simple and stablecircuit operation by realizing a test function through detection of avoltage higher than an over-charge detection voltage of a secondarybattery without providing a separate test terminal, thereby reducing acost. Another object of the present invention is to reduce a cost bysetting a plurality of test time shortening modes using a fuse.

The present invention provides a charging type power supply device,including: a plurality of over-charge detection circuits; a delaycircuit; and a charging and discharging switch control circuit, thecharging and discharging control circuit including: a detection circuitfor detecting a voltage higher than an over-charge detection voltage ofa secondary battery; and switching means for switching between a normalstate for controlling charging and discharging of the secondary batteryand a test state for evaluating a characteristic of the charging anddischarging control circuit based on outputs from the plurality ofdetection circuits.

In the charging type power supply device, the switching means sets thecharging and discharging control circuit to the test state when a firstdetection circuit of the plurality of detection circuits detects thevoltage higher than the over-charge detection voltage, and sets thecharging and discharging control circuit to the normal state when asecond detection circuit of the plurality of detection circuits detectsthe voltage higher than the over-charge detection voltage.

Further, acceleration means for increasing an oscillating frequency ofan oscillator circuit constituting a delay circuit when the charging anddischarging control circuit is in the test state is provided. Thecharging and discharging control circuit further includes a fuse andswitching is performed between stages of a counter circuit constitutingthe delay circuit based on presence or absence of the fuse when thecharging and discharging control circuit is in the test state.

As described above, according to the charging and discharging controlcircuit and the charging type power supply device in the presentinvention, switching between test functions is realized without addingan external control terminal, and the efficient use of a test time isrealized by setting a plurality of delay time modes in a test state.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 is a circuit diagram showing a charging and discharging controlcircuit according to an embodiment of the present invention;

FIG. 2 is a circuit diagram showing an example of a conventionalcharging and discharging control circuit; and

FIG. 3 is a table showing a relationship between a voltage appliedbetween battery connection terminals and a state and function of thecharging and discharging control circuit according to the embodiment ofthe present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Hereinafter, an embodiment of the present invention will be described indetail with reference to the accompanying drawings. FIG. 1 is a circuitdiagram for explaining a charging and discharging control circuitaccording to the embodiment of the present invention. In FIG. 1, thecharging and discharging control circuit includes an over-chargedetection comparator 101 for a battery cell-1, an over-charge detectioncomparator 102 for a battery cell-2, an over-discharge detectioncomparator 103 for the battery cell-1, an over-discharge detectioncomparator 104 for the battery cell-2, bleeder resistors 107 and 108 forover-charge detection, bleeder resistors 109 and 110 for over-dischargedetection, a circuit 111 for generating a reference voltage for thebattery cell-1, a circuit 112 for generating a reference voltage for thebattery cell-2, an OR circuit 113 for over-charge detection, an ORcircuit 114 for over-discharge detection, and an over-current detectioncircuit 120. The charging and discharging control circuit furtherincludes an oscillator circuit 121 having a clock cycle Tclk, a countercircuit 122, and a charging and discharging switch control circuit 123.The charging and discharging switch control circuit 123 causes acharging control switch and a discharging control switch to turn ON/OFFthrough a charging control output terminal COP and a discharging controloutput terminal DOP based on information including battery states andcharging and discharging currents. The charging control switch and thedischarging control switch are located between the secondary batteriesand external power supply terminals. The battery states and charging anddischarging currents are obtained by the over-charge detectioncomparator 101, the over-charge detection comparator 102, theover-discharge detection comparator 103, the over-discharge detectioncomparator 104, and the over-current detection circuit 120. Therefore, afunction for protecting the batteries is realized.

The charging and discharging control circuit further includes adetection comparator 105 for detecting a voltage higher than anover-charge detection voltage of the battery cell-1 and a detectioncomparator 106 for detecting a voltage higher than an over-chargedetection voltage of the battery cell-2 as shown in FIG. 1. Each of thevoltages detected by the detection comparators 105 and 106 is set to avalue higher than the over-charge detection voltage. In other words,each of the voltages is set in a high battery voltage range, which isimpossible in normal use.

As shown in FIG. 1, when the voltage higher than the over-chargedetection voltage is applied between battery connection terminals of thebattery cell-1 and simultaneously a voltage equal to or lower than aspecified voltage is applied between battery connection terminals of thebattery cell-2, the detection comparator 105 detects the voltage higherthan the over-charge detection voltage and simultaneously theover-discharge detection comparator 104 detects an over-discharge state.At this time, the detection comparator 106 and the over-dischargedetection comparator 103 detect none. Then, a latch circuit 117 is setthrough an AND circuit 115, so that a TEST signal becomes “H”.Therefore, the charging and discharging control circuit enters a teststate. The test state is kept until the TEST signal becomes “L”. Incontrast to this, when the voltage higher than the over-charge detectionvoltage is applied between the battery connection terminals of thebattery cell-2 and simultaneously the voltage equal to or lower than thespecified voltage is applied between the battery connection terminals ofthe battery cell-1, the detection comparator 106 detects the voltagehigher than the over-charge detection voltage and simultaneously theover-discharge detection comparator 103 detects the over-dischargestate. At this time, the detection comparator 105 and the over-dischargedetection comparator 104 detect none. Then, the latch circuit 117 isreset through an AND circuit 116, so that the TEST signal becomes “L”.Therefore, the test state of the charging and discharging controlcircuit is cancelled to return to a normal state. The normal state iskept until the TEST signal becomes “H”.

In the case of the normal state, the charging and discharging switchcontrol circuit 123 causes the charging control switch and thedischarging control switch to turn ON/OFF through the charging controloutput terminal COP and the discharging control output terminal DOPbased on the information including the battery states and the chargingand discharging currents. The battery states and charging anddischarging currents are obtained by the over-charge detectioncomparator 101, the over-charge detection comparator 102, theover-discharge detection comparator 103, the over-discharge detectioncomparator 104, and the over-current detection circuit 120. Because theTEST signal is “L”, the oscillator circuit is oscillated at a normaloscillating frequency. The clock cycle is Tclk. An output of a NANDcircuit 126 becomes “H”, so that an over-charge detection delay time andan over-discharge detection delay time each become a delay time obtainedfrom the counter circuit. For example, when the detection comparator 101detects the over-charge state of the battery cell-1, the oscillatorcircuit is oscillated. The clock cycle Tclk is sent to the countercircuit. The over-charge detection delay time is obtained from anm-stage Qm of the counter circuit, so that the over-charge detectiondelay time is represented by the following expression:Tc=2^(m−1) *Tclk  (Expression 1)When the over-charge detection delay time elapses, the charging anddischarging switch control circuit 123 causes the charging controlswitch to turn OFF through the charging control output terminal COP. Theover-discharge detection delay time is obtained from an n-stage Qn ofthe counter circuit, so that the over-discharge detection delay time isrepresented by the following expression:Td=2^(n−1) *Tclk  (Expression 2)When the detection comparator 103 detects the over-discharge state ofthe battery cell-1 and the over-discharge detection delay time elapses,the charging and discharging switch control circuit 123 causes thedischarging control switch to turn OFF through the charging controloutput terminal DOP. For example, assume that the clock cycle Tclk ofthe oscillator circuit is set to 300 μsec., the over-charge detectiondelay time is obtained from a fifteenth stage Q15 of the countercircuit, and the over-discharge detection delay time is obtained from atenth stage Q10 of the counter circuit. Therefore, according toExpressions 1 and 2, the over-charge detection delay time Tc becomes 4.9seconds and the over-discharge detection delay time Td becomes 154milliseconds.

On the other hand, in the case of the test state, the charging anddischarging switch control circuit 123 causes the charging controlswitch and the discharging control switch to turn ON/OFF through thecharging control output terminal COP and the discharging control outputterminal DOP based on the information including the battery states andthe charging and discharging currents. The battery states and chargingand discharging currents are obtained by the over-charge detectioncomparator 101, the over-charge detection comparator 102, theover-discharge detection comparator 103, the over-discharge detectioncomparator 104, and the over-current detection circuit 120. Because theTEST signal is “H”, the oscillator circuit is oscillated at anaccelerated oscillating frequency. When the oscillator circuit isaccelerated at a K-times higher oscillating frequency, the clock cyclebecomes Tclk/K. The output of the NAND circuit 126 is determinedaccording to the presence or absence of a fuse 124. Therefore, theover-charge detection delay time and the over-discharge detection delaytime can be obtained from the direct output of the oscillator circuit121 or the output of the counter circuit, which is selected byswitching.

In initial measurement for trimming to setting voltages for detectingthe over-charging and over-discharging and canceling, which is performedat the factory, the fuse 124 is not cut, so that the output of the NANDcircuit 126 becomes “L”. In this case, the over-charge detection delaytime and the over-discharge detection delay time are directly obtainedfrom the output of the oscillator circuit 121 by a logical circuit whichis composed of inverters 133 and 134 and NAND circuits 127, 128, 129,130, 131, and 132. Therefore, the over-charge detection delay time isrepresented by the following expression:Tc=Tclk/K  (Expression 3)and the over-discharge detection delay time is represented by thefollowing expression:Td=Tclk/K  (Expression 4)Because an over current delay time and all cancel delay times areobtained from the counter circuit, the cancel delay times are determinedaccording to only an acceleration factor of the oscillator circuit. Thisis referred to as a delay time mode 1. For example, when the clock cycleTclk of the oscillator circuit is set to 300 μsec. and an accelerationfactor K of the oscillator circuit is set to 50, the over-chargedetection delay time Tc and the over-discharge detection delay time Tdeach become 6 μsec. according to Expressions 3 and 4. In contrast to theover-charge detection delay time of several seconds in theabove-mentioned normal state, the over-charge detection delay time isonly several microseconds. Thus, when the over-charge detection voltagevalue is measured with precision, it is possible to significantlyshorten the test time.

In the cases of a secondary test and customer's evaluation, the fuse 124is cut, so that the output of the NAND circuit 126 becomes “H” by apull-down resistor 125. In this case, the over-charge detection delaytime and the over-discharge detection delay time are obtained from theoutputs of the counter circuit as in the normal state by a logicalcircuit which is composed of the inverters 133 and 134 and the NANDcircuits 127, 128, 129, 130, 131, and 132. At this time, the TEST signalis “H”, so that the oscillator circuit is accelerated at a K-timeshigher oscillating frequency. Therefore, the over-charge detection delaytime is represented by the following expression:Tc=2^(m−1) *Tclk/K  (Expression 5)and the over-discharge detection delay time is represented by thefollowing expression:Td=2^(n−1) *Tclk/K  (Expression 6)The over current delay time and all the cancel delay times are shortenedaccording to the acceleration factor of the oscillator circuit. This isreferred to as a delay time mode 2. For example, assume that the clockcycle Tclk of the oscillator circuit is set to 300 μsec. and theacceleration factor K of the oscillator circuit is set to 50. In thiscase, according to Expressions 5 and 6, the over-charge detection delaytime Tc becomes 98 milliseconds and the over-discharge detection delaytime Td becomes 3 milliseconds. Thus, when the over-charge detectionvoltage value and the over-discharge detection voltage value aremeasured, it is possible to not only shorten the delay times but alsoevaluate each of the delay times.

As described above, in the charging and discharging control circuit andcharging type power supply device of the present invention, switchingbetween the states is performed on a case-by-case basis as follows.

In the initial measurement for trimming to setting voltages fordetecting the over-charging and over-discharging and canceling, which isperformed at the factory, the fuse is not cut and a voltage higher thanthe over-charge detection voltage is inputted to a battery connectionterminal of the charging and discharging control circuit, which isconnected with a battery. Therefore, the charging and dischargingcontrol circuit can be set to the test state and the test state is keptby a holding circuit. In the test state, the oscillating frequency ofthe oscillator circuit composing the delay circuit becomes higher and anover-charge detection signal and an over-discharge detection signal donot pass through the counter circuit composing the delay circuit, sothat a delay time of the over-charge detection signal and a delay timeof the over-discharge detection signal each become the oscillating cycleof the oscillator circuit. Thus, even when the over-charge detectionvoltage and the over-discharge detection voltage are measured withprecision, a wait time is significantly shortened, so that the test timecan be significantly shortened. In the delay time mode 1, each of delaytimes of other signals (over-current detection delay time and all canceldelay times) becomes a time for which a signal shortened by theaccelerated oscillating frequency of the oscillator circuit passesthrough the counter circuit composing the delay circuit.

In the cases of the secondary test and customer's evaluation, the fuseis cut and a voltage higher than the over-charge detection voltage isinputted to a battery connection terminal of the charging anddischarging control circuit. Therefore, the charging and dischargingcontrol circuit can be set to the test state, and the test state is keptby a holding circuit. In the test state, the oscillating frequency ofthe oscillator circuit composing the delay circuit becomes higher.However, each of all signals including the over-charge detection signaland the over-discharge detection signal corresponds to a delay time forwhich each of the signals passes through the counter circuit composingthe delay circuit. In the delay time mode 2, the test times formeasuring the over-charge detection voltage value, the over-dischargedetection voltage value, and the over-current detection voltage valuecan be shortened and the evaluation between the respective delay timescan be performed.

Then, when the voltage higher than the over-charge detection voltage isinputted to another battery connection terminal of the charging anddischarging control circuit, the test state kept by the holding circuitis canceled. Therefore, the charging and discharging control circuitreturns to the normal state. In this state, all the signals includingthe over-charge detection signal and the over-discharge detection signalwith delay times are sent to the charging and discharging switch controlcircuit through the counter circuit composing the delay circuitregardless of the presence or absence of the fuse. Thus, each of thedelay times of all the signals including the over-charge detectionsignal and over-discharge detection signal becomes the delay time in thenormal state.

FIG. 3 is a table showing a relationship between the voltage appliedbetween the battery connection terminals and the state and function ofthe charging and discharging control circuit.

1. A charging and discharging control circuit equipped with a pluralityof over-charge detection circuits for monitoring a plurality ofsecondary batteries, a delay circuit for generating a delay time inresponse to outputs from the over-charge detection circuits, and acharging and discharging switch control circuit for controlling a switchcircuit in response to the outputs from the over-charge detectioncircuits and an output from the delay circuit, the charging anddischarging control circuit comprising: a plurality of detectioncircuits for detecting a voltage higher than an over-charge detectionvoltage of each of the secondary batteries; and a circuit for switchingbetween a normal state for controlling charging and discharging of thesecondary batteries and a test state for evaluating a characteristic ofthe charging and discharging control circuit in response to signals fromthe plurality of detection circuits.
 2. A charging and dischargingcontrol circuit according to claim 1, wherein the charging anddischarging control circuit is set to the test state when a firstdetection circuit of the plurality of detection circuits detects thevoltage higher than the over-charge detection voltage.
 3. A charging anddischarging control circuit according to claim 2, wherein the chargingand discharging control circuit is set to the normal state when a seconddetection circuit of the plurality of detection circuits detects thevoltage higher than the over-charge detection voltage.
 4. A charging anddischarging control circuit according to claim 1, further comprising aholding circuit for holding a state of the charging and dischargingcontrol circuit.
 5. A charging and discharging control circuit accordingto claim 1, wherein the delay circuit comprises an oscillator circuitand the charging and discharging control circuit further comprisesacceleration means for increasing an oscillating frequency of theoscillator circuit when the charging and discharging control circuit isin the test state.
 6. A charging and discharging control circuitaccording to claim 1, wherein the delay circuit comprises a countercircuit and the charging and discharging control circuit furthercomprises a fuse and delay time mode switching means for switchingbetween stages of the counter circuit based on presence or absence ofthe fuse when the charging and discharging control circuit is in thetest state.
 7. A charging type power supply device, comprising: a switchcircuit and a secondary battery which are connected in series with anexternal power supply terminal; and the charging and discharging controlcircuit according to claim 1, which is connected in parallel with thesecondary battery to control the switch circuit.